Hydrocephalus comes from the Greek: hydro means water, cephalus means head. Hydrocephalus is an abnormal accumulation of fluid--cerebrospinal fluid ("CSF") within cavities called ventricles, inside the brain. CSF is produced in the ventricles, circulates through the ventricular system, and is absorbed into the bloodstream. CSF is reabsorbed at a rate that is dependent on regulation of intracranial pressure ("ICP"). CSF is in constant circulation and has many important functions. It surrounds the brain and spinal cord and acts as a protective cushion against injury. CSF contains nutrients and proteins that are needed for the nourishment and normal function of the brain. It also carries waste products away from surrounding tissues. Hydrocephalus occurs when there is an imbalance between the amount of CSF that is produced and the rate at which it is absorbed. As the CSF builds up, it causes the ventricles to enlarge and the pressure inside the head to increase. Congenital Hydrocephalus is thought to be caused by a complex interaction of genetic and environmental factors. Aqueductal stenosis, an obstruction of the cerebral aqueduct, is the most frequent cause of congenital hydrocephalus. Acquired hydrocephalus may result from spina bifida, intraventricular hemorrhage, meningitis, head trauma, tumors and cysts. Hydrocephalus affects about one in every 500 children born.
There is no known way to prevent or cure hydrocephalus. To date, the most effective treatment is surgical insertion of a shunt. A shunt is a flexible tube placed into the ventricular system of the brain which diverts the flow of CSF into another region of the body, most often the abdominal cavity or a chamber of the heart, where it can be absorbed. A valve within the shunt attempts to maintain the CSF at a pre-estimated ICP by allowing the valve to open in response to that pressure level. Under most circumstances, no specific testing is performed in advance of surgery to try and estimate the patient's flow needs. Since the flow needs are not determined prior to the insertion of the shunt, more surgery may be necessary in the future to fit a matching valve for the patient.
A shunt is simply a drain, which diverts the accumulated CSF from the obstructed pathways and returns it to the bloodstream. The device consists of a system of tubes with a valve to control the rate of drainage and prevent back-flow. It is inserted surgically so that the upper end is in a ventricle of the brain and the lower end leads either into the heart (ventriculo-atrial, FIG. 2A) or into the abdomen (ventriculo-peritoneal, FIG. 2B). The device is completely enclosed so that all of it is inside the body. Other drainage sites such as the outer lining of the lungs (ventriculo-pleural shunt) can also be used. In most cases, the shunts are intended to stay in place for life, although alterations or revisions might become necessary from time to time.
Today, there are numerous types of shunts but while different in appearance they work in a very similar manner. None can be said to be significantly better or worse than others, and the shunt is usually chosen by the surgeon based on experience, cost and personal preference. Special in-hospital 24-hour monitoring can be utilized to evaluate the degree of shunt dependency and ICP requirements. The hospital monitoring is expensive, complicated, and is usually only a last resort effort when the patient condition is quite severe.
Originally, shunts were inserted so that a tube drained CSF from the ventricles in the brain, through the valve and through another tube into a vein in the neck and then into the heart (FIG. 2A). While these are still used, most currently drain the CSF into the abdomen (FIG. 2B) and the bottom tube can be felt over the ribs. Despite all these developments, shunting can have complications. These can be divided into under-drainage, over-drainage and infection. The treatment involves operations, often indeterminate hospital stays and disappointing relapses before a successful outcome could eventually be realized. There is a need for a way to monitor hydrocephalus patients during their daily routines after having a shunt implantation as to better evaluate the performance of the shunt and valve matching for the patient.